This invention relates to a method of making complex microspheres, complex microspheres made by such a method and thermoplastic films containing such complex microspheres.
It has been known to add complex microspheres to paints, cosmetic products, rubbers, plastics, paper and the like during their production or fabrication processes in order to improve their properties or, more specifically, to thermoplastic films during their production or fabrication process in order to modify their properties. Nowadays, polyolefin, polyester, polyvinyl chloride, polyamide, polystyrene and many other kinds of thermoplastic films are widely being used as industrial base films, for example, as lapping material, for photography, as magnetic memory media and as capacitors. With the recent demands for higher performance and greater variety of these base films, however, it is becoming of vital importance to further improve the surface characteristics of these films. In the field of magnetic memory media using a base film produced from a resin composition having linear aromatic polyester as its principal element, for example, there is a strong demand not only regarding its thickness but also for improved lubricity because of the requirement of high memory density, high capacity and high reliability. In the field of lapping materials using base films of a resin composition having polyolefin as its principal element, as another example, there is a strong requirement for anti-blocking characteristics because the surfactants and water-soluble macromolecules which are applied to the film for providing improved antistatic, printable and anticloud properties tend to enhance the blocking between the film surfaces.
In the past, use of particles of different kinds such as polystyrene, polyvinyl acetate, polyethylene, nylon, epoxy resins, phenol resins and polysiloxane has been proposed. As examples of polysiloxane particles, use of silica particles (i. Colloid and Interface Sci. , Vol. 26, 62-69, 1968), polymethylsilsesquioxane particles (Japanese Patent Publication Tokkai 63-77940), and polyorganosiloxane particles (Japanese Patent Publication Tokkai 63-312324) has been proposed. Regarding the modification of thermoplastic films by the application of such polysiloxane particles, Japanese Patent Publication Tokkai 59-171623 reported improved lubricity by their application onto a polyester film.
There are problems with these prior art particles. Firstly, they are easily breakable by a mechanical impact. Secondly, they do not disperse easily inside a medium or a polymer material. Thirdly, their dispersion stability is poor. Fourthly, their shapes and size distribution are not uniform. These problems make it difficult as a matter of fact to accomplish the desired modification of a film. In other words, even if polysiloxane particles of the kinds which have been suggested are applied to a thermoplastic film, the kind of improved lubricity and anti-blocking properties which is recently being required of thermoplastic films cannot be realized without adversely affecting their basic original characteristics.